Debug mode:

Hold LS and press A, B, Right, A, C, A, Down, A, B, Right, A at the 
Annex room with the two doors. An option menu will appear. Press X 
to exit the debug menu after the desired options have been selected. 
If cheats are used in the Campaign Missions, they will be kept in 
the saved game, with no opportunity to turn them off. 

Invincible player
Set to "Yes" to allow the currently controlled terminator to be 
invincible. 

Invincible terminators
Set to "Yes" to allow all terminators to be invincible. 

Easy close assault
Note that the terminators still may be killed even if this is set at 
"Yes". 

Player always wins
Set to "Yes" to allow the current mission to be completed 
successfully, even if all objectives are not met or the squad is 
killed. 

No new stealers
Set to "Yes" to prevent the genestealer generators from producing 
reinforcements. 

Infinite freeze time
Unlimited time for strategy mode. 

Infinite ammo
Unlimited ammunition for all weapons. 

No jams or malfunctions
Prevent bolters from jamming and flamer throwers from exploding. 

Campaign
Allow any campaign mission to be played. Games played from this 
option cannot be saved.